Up till recently, nuclear reactors have been built directly inside vessels, the reactors being assembled part by part using the hoisting machines usually emloyed in shipyards.
Some of the parts constituted undividable masses weighing several hundreds of metric tons. The result is that it has been practically impossible to envisage building a vessel propelled by nuclear power except in those few shipyards which have exeptionally powerful hoisting means available.
Further, such building of a nuclear reactor on board a vessel has required a very long time performance and has occupied the ship-building dock for an excessively long period. This has disorganized the construction program and incurred prohibitive costs.
Lastly, the working conditions when assembling reactors on board vessels have been unsatisfactory, in particular in so far as work could not be performed in conditions of real nuclear cleanliness.
That is why, in accordance with a known method, it has been proposed to form vessels in two prefabricated floating parts which are subsequently assembled together, one of the parts including a chamber in which a nuclear reactor block is inserted by a horizontal translation movement before the two parts are assembled together. A complex operation is required to install the nuclear reactor because of its bulk and its weight (several thousands of metric tons).